Many different types of printing have been invented, a large number of which are presently in use. The known forms of printers have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and inkjet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of inkjet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on inkjet printing have been invented. For a survey of the field, reference is made to an article by J Moore, "Non-Impact Printing: Introduction and Historical Perspective", Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Inkjet printers themselves come in many different types. The utilisation of a continuous stream ink in inkjet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static inkjet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous inkjet printing including the step wherein the inkjet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al).
Piezo-electric inkjet printers are also one form of commonly utilized inkjet printing device. Piezo-electric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezo electric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezo-electric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a Piezo electric push mode actuation of the inkjet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a sheer mode type of piezo-electric transducer element.
Recently, thermal inkjet printing has become an extremely popular form of inkjet printing. The inkjet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed inkjet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
Recently, the present applicant has disclosed for example, an Australian Provisional Patent No. PP6534 entitled "Micromechanical Device and Method (IJ46a)", filed Oct. 16, 1998 a new form of inkjet printer containing an ink ejection mechanism that includes a thermal bend actuator actuated in an external ambient environment which is interconnected with a paddle mechanism utilised for the ejection of ink.
Unfortunately, in the aforementioned inkjet printing arrangement as in most inkjet printing arrangements, there is a tendency of the ink ejection nozzles to dry out over time which can result in the build up of crustaceans etc. Further, there is also the propensity of such devices to become clogged by other means such as foreign bodies in the ink or paper fibers, material etc. around the ink ejection nozzle.
Further, in the aforementioned arrangement, there is a significant gap left in one wall of the ink ejection chamber, the gap being required and utilized by the movement of the thermal actuator up and down during an ejection cycle. Unfortunately, the provision of the slot may cause ink flow to wick out of the nozzle chamber and along the thermal actuator which can cause problems with ink loss due to wicking. Such ink loss is generally undesirable.